1. Field of the Invention
The invention relates to a process for the deposition of copper on a support, in particular for integrated circuits.
2. Description of the Related Art
The use of copper for producing electrical contacts in integrated circuits is justified by its low electrical resistivity and its low electromigration.
It is known to deposit thin layers on supports by a PVD (physical vapor deposition) process or by a CVD (chemical vapor deposition) process. CVD gives more even deposits as the first stage is an absorption stage which is not directional.
Various processes for the deposition of copper layers employing CuCl precursors have been provided in the prior art:    J. C. A. Boyens et al. (S. Afr. J. Chem., 1986, 39(4), 229) disclose a ((COD)CuCl)2 complex prepared by diffusion of SO2 into a solution of CuCl2.2H2O and 1,5-cyclooctadiene (COD) in ethanol. The complex is characterized by an X-ray crystal structure obtained from a monocrystal and it is used in photoreactions.    N. Bourhila et al. [Appl. Surf. Sci., 91 (1–4), 175–181 (1995)] disclose the use of (CuCl)3 for the deposition of Cu films by CVD in a low-pressure reactor. The process is an in situ chloridation of Cu by Cl2 which results in the deposition of copper by the reduction of Cu3Cl3 by hydrogen in the reactor. The purpose of the studies was to find a Cu precursor capable of replacing Cu precursors in the solid form, which present a problem in controlling the vapor pressure during the deposition. The solution provided consists in synthesizing the precursor immediately above the surface on which Cu has to be deposited. The disadvantage of this process is that it deposits a Cu film both on the support to be covered and on the walls of the reactor, which it is subsequently necessary “to clean”.
Other processes employing precursors of the diketonate type have also been provided:    P. Doppelt and T. H. Baum (MRS Bull., XIX (8), (1994) 41) provide a process for the deposition of copper films by CVD on supports for the preparation of electrical contacts in integrated circuits, for the preparation of electronic components with metal lines of less than 0.25 μm. The copper precursors mentioned are in particular complexes in which Cu is coordinated by an acetylacetonate (acac) group, a trifluoroacetylacetonate (tfac) group or a hexafluoroacetylacetonate (hfac) group and stabilized by various ligands, in particular COD or DMCOD (1,5-dimethyl-1,5-cyclooctadiene) ligands.    FR-2 760 743 (or U.S. Pat. No. 6,130,345) discloses various copper precursors for the deposition of copper by CVD, in particular CU(I) coordination complexes stabilized by a ligand, in which Cu is coordinated by a β-diketonate, in particular by a hexafluoroacetylacetonate, and stabilized by various ligands.    Chen et al. [Chem. Mat., 13, 3993 (2001)] disclose copper precursors, of the diketonate type, stabilized by 2-methyl-1-hexen-3-yne. They are in particular Cu(acac)MHY, Cu(tfac)MHY, Cu(hfac)MHY and Cu(pfac)MHY. MHY is 2-methylhex-3-yne. The process employs a low-pressure CVD reactor into which a mixture of Cu(hfac)MHY precursor (which is a liquid) and of pure MHY (95/5) is injected in the liquid form. In view of the respective proportions of the constituents, this is not a solution of the complex in MHY. MHY acts simply to reduce the viscosity of the liquid complex.    U.S. Pat. No. 5,096,737 discloses the use of Cu(I) complexes as precursors for the deposition of copper by CVD. The complexes are formed by Cu(I) coordinated to a β-diketonate and are stabilized by a ligand. The β-diketonate can be, for example, acac, tfac or hfac. The ligand can be an alkyne, an olefin, a diene or a phosphine, for example COD or DMCOD. The DMCOD(Cu(I))(hfac) precursor is introduced into the CVD reactor by bubbling argon through the liquid precursor.    U.S. Pat. No. 5,098,516 discloses a process for the deposition of a copper film on a support by bringing said support into contact, at a temperature between 110° C. and 190° C., with an organometallic copper complex coordinated by a β-diketonate (in particular hfac) stabilized by a ligand. The precursor is chosen for its volatile nature and can thus be introduced into the reactor in the gaseous form.    U.S. Pat. No. 5,085,731 and U.S. Pat. No. 5,144,049 disclose copper complexes which can be used for the deposition of copper films by CVD. The complexes are volatile liquid organo-metallic complexes coordinated by a fluorinated acetyl-acetonate and stabilized by a ligand. For the implementation of the CVD, the precursor is introduced into the reactor in the form of a pure precursor vapor or is entrained by argon towards the reactor by bubbling argon through the liquid precursor.
However, the use of these complexes of copper which is coordinated by a β-diketonate for the deposition of a copper film exhibits a major disadvantage: the heteroatoms present in the ligands are reencountered in the form of contaminants in the deposited copper film.
In addition, provision has been made for the deposition of copper films by a CVD process using a precursor solution. For example, WO 98/00432 discloses a process for the deposition of a metal layer by CVD starting from a solution of a platinum complex using a liquid injector. Such a process is advantageous technically but it can be employed only with precursor complexes which are readily soluble in the solvents which can be used in liquid injectors.